1. FIELD OF THE INVENTION
This invention relates to new and useful improvements in drill bits and more particularly to drill bits having replaceable nozzles and improved retaining means therefor.
2. BRIEF DESCRIPTION OF THE PRIOR ART
Rotary drill bits used in earth drilling are primarily of two major types. One major type of drill bit is the roller cone bit having three legs depending from a bit body which support three roller cones carrying tungsten carbide teeth for cutting rock and other earth formations. Another major type of rotary drill bit is the diamond bit which has fixed teeth of industrial diamonds supported on the drill body or on metallic or carbide studs or slugs anchored in the drill body.
It is well known in both types of drill bit to provide nozzle passages for circulating drilling fluid from the interior of the drill bit in a jet toward the point where the cutters engage the bottom of the hole. In roller cone type bits there has been a substantial amount of activity, mostly in the 1950s and 60s, in the development of removable nozzles. In diamond type drill bits, most bit bodies have been provided with fixed nozzle passages. Removable nozzles have been difficult to apply to diamond drill bits because of the proximity of the nozzle to the cutting surface which results in a very rapid erosion of the snap ring retainers for the nozzle members.
Replaceable nozzles have been developed in the past. These nozzles have been retained in a fluid discharge bore in the bit body by abutting their upper ends against shoulders in the bore and then inserting snap rings into grooves at the lower end of the nozzle. The drilling fluid is very abrasive and the exposure of the snap rings as well as the bit body at the lower end of the nozzle adjacent to the snap ring groove to the wash of the drilling fluid has caused this snap ring as well as the body portion supporting it to erode and fail, permitting the nozzle to be lost into the bottom of the hole.
This structural arrangement, wherein the snap ring and its support are continually exposed to drilling fluid, together with the fact that higher drilling fluid jet velocities and consequently high pressure differentials across the nozzle are being used, combined to make the snap ring somewhat unsatisfactory in many cases for retaining nozzles in the bit body. A variety of patents have been granted on arrangements which attempt to solve this problem in roller cone bits.
Payne U.S. Pat. No. 2,855,182 discloses a replaceable nozzle for a roller cone type bit which is provided with a peripheral sealing ring and is held in place by a snap ring adjacent the discharge end of the nozzle.
Sease U.S. Pat. No. RE. 25,452 (of 2,868,512) discloses a nozzle which is substantially the same as that shown in Payne but provided with a rubber sealing ring protecting the end of the nozzle against abrasion.
Scarborough U.S. Pat. No. 3,084,751 discloses a roller cone bit having replaceable nozzles secured in position by retaining pins located away from the abrasive environment at the end of the nozzle. This structure is somewhat difficult to manufacture.
Steen U.S. Pat. No. 3,096,834 discloses a replaceable jet nozzle for rock bits having a rubber shield at the lower face of a metal retainer ring.
Mandrell U.S. Pat. No. 3,115,200 discloses a removable nozzle for a drill bit having an improved arrangement for accessibility of a snap ring for retaining the nozzle in place.
Crawford U.S. Pat. No. 3,137,354 discloses removable drill bit nozzles secured in place by set screws.
Neilson U.S. Pat. No. 3,207,241 discloses removable drill bit nozzles secured in place by threaded retaining sleeves.
The copending application Ser. No. 220,306, filed Dec. 29, 1980, discloses an improved arrangement for securing replaceable nozzles in drilling bits by means of a metal or hard metal retaining ring.
There are several types of diamond bits known to the drilling industry. In one type, the diamonds are a very small size and randomly distributed in a supporting matrix. Another type contains diamonds of a larger size positioned on the surface of a drill shank in a predetermined pattern. Still another type involves the use of a cutter formed of a polycrystalline diamond supported on a sintered carbide support.
Some of the most recent publications dealing with diamond bits of advanced design, relavent to this invention, consists of Rowley, et al. U.S. Pat. No. 4,073,354 and Rohde, et al. U.S. Pat. No. 4,098,363. An example of cutting inserts using polycrystalline diamond cutters and an illustration of a drill bit using such cutters, is found in Daniels, et al. U.S. Pat. No. 4,156,329.
The most comprehensive treatment of this subject in the literature is probably the chapter entitled STRATAPAX bits, pages 541-591 in ADVANCED DRILLING TECHNIQUES, by William C. Maurer, The Petroleum Publishing Company, 1421 South Sheridan Road, P. O. Box 1260, Tulsa, Okla., 74101, published in 1980. This reference illustrates and discusses in detail the development of the STRATAPAX diamond cutting elements by General Electric and gives several examples of commercial drill bits and prototypes using such cutting elements.
These patents and the cited literature show the construction of various diamond bits and related prior art but do not consider the problem of nozzle retention in diamond bits adjacent to the cutting surface of the bit.